correlation is not causation

"Early studies that looked at the Internet and social involvement suggested that people who were heavy users of the Internet were also those who reported greater feelings of loneliness and social isolation. More recent surveys, however, have discovered just the opposite. One survey found that Internet use was related to more social involvement in the local community; another found that those who spent a great deal of time on the Internet were more politically involved and had more contacts than those who did not spend time online. Yet another found that Internet users were the ones with the most social contacts. Apparently, both the audiences and the Internet have changed over the past few years, and innovations such as instant messaging encourege greater social contact. Not all demographic groups, however, are benefiting from the expanding Internet. One 2004 study revealed that Internet use had no impact on social involvement or psychological well-being among low-income Americans.

All in all, surveys that have studied people's Internet use support the "rich gets richer" model. Extroverted people are the ones who gain the most social contacts through the Internet. To them, it is just another channel to use to link up with friends. Conversely, introverted people who go online tend to shy away from social contacts."

Reference:
Mass Media in a Changing World, Second Edition, 2009 Update
Rodman, G.